1. Field of the invention.
The present invention generally relates to mechanical presses and, more particularly, to a hydraulic overload relief system that remotely sets and controls the hydraulic relief pressure.
2. Description of the related art.
Mechanical presses, for example, stamping presses and drawing presses, comprise a frame having a crown and a bed and a slide supported within the frame for motion toward and away from the bed. The slide is driven by a crankshaft having a connecting rod or shutheight mechanism connected to the slide. Such mechanical presses are widely used for stamping and drawing operations and vary substantially in size in available tonnage depending upon the intended use.
In prior art presses of this type, the slide is generally connected to the crankshaft of the press drive by a connecting rod which is adjustable in length. Some systems utilize another member, such as a connection screw that is adjustable in its relationship to the slide so that the shutheight opening between the slide and the bed may be adjusted to accommodate various die sets. Disposed between these portions are chambers that are filled with pressurized hydraulic fluid at a system pressure that normally corresponds to the maximum force the press is expected to encounter during operation. During press operation, there is a necessity to limit the overall system pressure encountered by the press slide during the pressing operation to prevent damage to both the press and associated die sets. These systems to reduce or limit pressure are typically called overload systems in that they limit or prevent press overloading by exhausting the hydraulic fluid from the above-described chambers.
Prior chambers as described either were connected to pneumatic or hydraulic adjustment mechanisms to essentially disengage the slide from the drive mechanism of the press to reduce stamping pressure when the chambers were exhausted. These prior art overload systems were carried upon the slide and were subjected to stamping shock. The designs additionally had only a single large valve mounted centrally along the slide that was connected via hard pipe to the chambers within connection rods or screws. These parts would physically ride up and down along with the slide during operation. All of the previous overload systems utilized manually operated valves to control the hydraulic pressures therein.